The present invention relates to a cutting tool employing indexable cutting inserts and in particular a ball nose end mill employing such inserts.
End mills employing cutting inserts mounted at the front end of the tool are known in the art. The end mills can be used in several types of applications depending on the configuration of the cutting inserts mounted therein. The cutting inserts may present a peripheral cutting edge for side milling, a front cutting edge for face milling and a curved cutting edge of a so-called xe2x80x9cball-nosexe2x80x9d end mill for various copying applications.
In a ball-nose end mill or in another type of end mill where it is often required that the tool be able to cut up to the tool axis as shown, for example in U.S. Pat. No. 4,525,110 to Stojanovski, one cutting insert is located so as to present a cutting edge that extends to the axis of the tool and another cutting insert is located so as to present another cutting edge spaced away from the axis of the tool. The fact that in such cases two identical cutting inserts are located at different distances from the axis, can give rise to balancing problems.
When locating two cutting inserts in the front end of a ball-nose end mill another problem arises. This problem involves the fact that the cutting inserts are subjected to cutting forces in various directions, such forces tend to withdraw the cutting inserts from their pockets. A solution to this problem can be found, for example, in U.S. Pat. No. 4,808,045 to Tsujimura et al. In ""045, a groove of a channel-shaped cross-section is formed in a central portion of the lower surface of the insert. The side walls of the groove form abutment surfaces which receive component forces of the cutting feed from the inner and outer peripheral cutting edges. However, in ""045 the cutting inserts do not reach the axis of the tool.
Another solution of giving additional support to the cutting inserts can be found, for example, in U.S. Pat. No. 5,542,795 to Mitchell. In ""795, each cutting insert 36 is provided with an integrally formed rail 50 formed on the back face 40 of the cutting insert. A bottom wall 28 of each insert seat 26 includes a longitudinally oriented slot 32 for receiving the rail 50. Since, when tightening the locking screw 53, the cutting insert is pressed also against a sidewall 30 of the insert seat 26, the cutting tool of ""795 is not suitable for mounting identical cutting inserts near the axis of the tool since they require a sufficient thickness of radial support by the sidewall 30. It is understood that if the radial support between the two identical cutting inserts is made thin in order to locate the cutting inserts as close as possible to the axis of the tool, then the central portion of the tool becomes week.
In Japanese patent JP 8206910 to Takuya it is shown how to retain a cutting insert having a stepped convex part 18 in its bottom within a stepped concave part 27 formed inside the insert seat. However, ""910 does not teach how to retain two cutting inserts that cut till the axis of the tool.
It is the object of the present invention to provide an end mill that significantly reduces or overcomes the aforementioned disadvantages.
It is a further object of the present invention to provide a ball-nose end mill having two identical and indexable cutting inserts.
In accordance with the present invention there is provided a cutting tool (20, 82) comprising a tool body (22, 22xe2x80x2) and two cutting inserts (24, 24a, 24b) mounted therein;
the tool body having two insert receiving pockets (26, 26a, 26b) substantially symmetrically located with respect to a center line of the tool body, each of the two insert receiving pockets comprising:
a pocket base wall (30),
an indentation (32) opening to the base wall, the indentation having a lower wall (34) that is connected to at least three side walls, a first side wall (36) of said at least three side walls being substantially longitudinally directed with respect to the center line, a second side wall (38) of said at least three side walls being parallel to the first side wall and located more distantly relative to the first side wall with respect to the center line of the tool body, a third side wall (40) of said at least three side walls being transversely directed with respect to the first and second side walls,
a threaded bore (54) extending through the lower wall (34) of the indentation (32);
each of the two cutting inserts (24, 24a, 24b) comprising:
a rake surface (62), an insert base wall (68) and a peripheral relief surface (63) connecting the rake surface and the base wall, and cutting edges (59, 60) defined between the rake and relief surfaces,
a protuberance (69) extending downwardly from the insert base wall (68) and away from the rake surface (62), the protuberance having a lower wall (70) that is connected to four lateral walls, each lateral wall being connected to an adjacent lateral wall, the four lateral walls being connected to the insert base wall, a first lateral wall (72) of the four lateral walls being substantially longitudinally directed with respect to the center line, a second lateral wall (73) of said four lateral walls being parallel to the first lateral wall, a third lateral wall (74) of the four lateral walls being transversely directed with respect to the first and second lateral walls, a fourth lateral wall (75) of the four lateral walls being parallel to the third lateral wall,
a through bore (58), having an axis (B), extending between the rake surface (62) and the lower wall (70);
each cutting insert is retained in a respective insert receiving pocket by a clamping screw (78) passing through the through bore (58) of the cutting insert and threadingly engaging the threaded bore (54), the insert base wall (68) abuts the pocket base wall (30) of the insert receiving pocket, the first lateral wall (72) of the protuberance abuts the first side wall (36) of the indentation (32), and the third lateral wall (74) of the protuberance (69) abuts the third side wall (40) of the indentation,
in a cross section taken perpendicular to the center line and passing through the threaded bores, the first lateral wall of the protuberance is distanced from the center line by a first distance D1 and the cutting edges are distanced from the center line by a second distance D2 and a third distance D3, where the third distance D3 is greater than the second distance D2, where the first distance D1 is at least three times greater than the second distance D2, and where the relief surface (63) is relieved from the insert receiving pocket (26, 26a, 26b).
Typically, the indentation (32) of the insert receiving pocket (26) is bounded by the first, the second, the third and a fourth side walls (36, 38, 40, 44), the first and the second side walls (36, 38) are parallel to each other and substantially longitudinally directed with respect to the center line, the third and the fourth side walls (40, 44) are parallel to each other and transversely directed with respect to the first and second side walls.
Preferably, the two cutting inserts (24) are identical.
According to a first embodiment of the present invention, the cutting tool having rotational symmetry with respect to the center line.
According to a second embodiment of the present invention, the two cutting inserts (24a, 24b) having mirror symmetry with respect to the center line in a top view of the cutting inserts.
Preferably, each cutting insert (24, 24a, 24b) has 180xc2x0 rotational symmetry around the axis of the through bore (58).
If desired, the indentation (32) is completely enclosed by four side walls (36, 38, 40, 44).
Typically, the first and second lateral walls (72, 73) of the protuberance (69) are perpendicular to the third and fourth lateral walls (74, 75) of the protuberance and the first and second side walls of the indentation (32) are perpendicular to the third and fourth side walls of the indentation.
Further typically, the first and second lateral walls (72, 73) of the protuberance are perpendicular to the insert base wall (68).
Further typically, the third and fourth lateral walls (74, 75) of the protuberance are perpendicular to the insert base wall (68).
Still further typically, the first and second side walls (36, 38) of the indentation are perpendicular to the pocket base wall (30).
Still yet further typically, the third and fourth side walls (40, 44) of the indentation are perpendicular to the pocket base wall (30).
In accordance with the present invention there is provided a tool body (22, 22xe2x80x2) having two insert receiving pockets (26, 26a, 26b) substantially symmetrically located with respect to a center line of the tool body, each of the two insert receiving pockets comprising:
a pocket base wall (30),
an indentation (32) opening to the base wall, the indentation having a lower wall (34) that is connected to at least three side walls, a first side wall (36) of said at least three side walls being substantially longitudinally directed with respect to the center line, a second side wall (38) of said at least three side walls being parallel to the first side wall and located more distantly relative to the first side wall with respect to the center line of the tool body, a third side wall (40) of said at least three side walls being transversely directed with respect to the first and second side walls,
a threaded bore (54) extending through the lower wall (34) of the indentation.
Preferably, at least one of the insert receiving pockets having a pocket side wall (27) substantially parallel to the center line and adjacent thereto, in a cross section taken perpendicular to the center line and passing through the threaded bores, the first side wall (36) of the indentation (32) is distanced from the center line by a fourth distance D4 and the pocket side wall (27) is distanced from the center line a fifth distance D5, where the fourth distance D4 is at least three times greater than the fifth distance D5.
According to a first embodiment of the present invention, the insert receiving pockets are rotationally symmetrical with respect to the center line.
According to a second embodiment of the present invention, the insert receiving pockets having substantially mirror symmetry with respect to the center line in a top view of the insert receiving pockets.
According to the present invention there is provided a cutting insert (24, 24a, 24b) comprising:
a rake surface (62), an insert base wall (68) and a peripheral relief surface (63) connecting the rake surface and the base wall, and cutting edges (59, 60) defined between the rake and relief surfaces,
a protuberance (69) extending downwardly from the insert base wall (68) and away from the rake surface (62), the protuberance having a lower wall (70) that is connected to four lateral walls, each lateral wall being connected to an adjacent lateral wall, the four lateral walls being connected to the insert base wall, a first lateral wall (72) of the four lateral walls being substantially longitudinally directed with respect to the center line, a second lateral wall (73) of said four lateral walls being parallel to the first lateral wall, a third lateral wall (74) of the four lateral walls being transversely directed with respect to the first and second lateral walls, a fourth lateral wall (75) of the four lateral walls being parallel to the third lateral wall,
a through bore (58), having an axis (B), extending between the rake surface (62) and the lower wall (70).
Preferably, the cutting insert having 180xc2x0 rotational symmetry around the axis of the through bore.
Typically, each of the cutting edges having a straight portion connected to a rounded portion.